The invention relates generally to a biosensor based on amplification by weak quantum measurements. In particular, the, biosensor uses the Aharonov-Albert-Vaidman (AAV) effect to amplify the surface plasmon resonance (SPR) enhanced Goos-Hänchen (GH) effect (hereafter, this biosensor can be referred to as the hybrid SPR/GH/AAV biosensor, or more simply as the hybrid biosensor.
The GH effect constitutes the small undetectable splitting of a polarized laser beam in response to total internal reflection of the beam. A thin gold film, disposed upon the surface of a total internal reflection prism, provides an SPR enhancement of the GH effect, i.e., the film increases the splitting of the incident laser beam. This splitting is proportional to the concentration of bio-molecules adhering to the gold film, i.e., the greater the concentration, the greater the splitting. Although this splitting is small for low concentrations of bio-molecules, application of the AAV effect can amplify the splitting. The hybrid sensor thereby enables the detection of extremely small heretofore undetectable concentrations of bio-molecules.
Optical biosensors are used to identify unknown biological hazards to facilitate effective mitigation upon discovery. A summary of such conventional devices is presented by X. Fan et al., “Sensitive Optical Biosensors for Unlabeled Targets: A Review”, Analytics Chemica Acta 620, 8-26 (2008), available at http://www.bme.umich.edu/labs/fanlab/files/prj13 2008/sensitive_optical_biosensors_for_u nlabeled_targets_a_review.pdf.
Signal amplification by the Aharonov-Albert-Vaidman (AAV) effect, has been used for measurement augmentation based on the weak value Aw of a quantum mechanical observable operator Â. The AAV effect is described by Y. Aharonov at al., “How the Result of a Measurement of a Component of the Spin of a Spin— 1/2  Particle Can Turn Out To Be 100”, Phys. Rev. Lett. (1988) 60, 1351- 1354, available at http://www.tau.ac.il/˜vaidman/lvhp/m8.pdf or else http://prl.aps.org/pdf/PRL/v60/i14/p1351—1 for details.
Further information on the AAV effect can be found in Y. Aharonov et al. “Properties Of A Quantum System During The Time Interval Between Two Measurements”, Phys. Rev. A 41, 11-20 (1990) available for example at http://xa.yimg.com/kq/groups/2385221/367896748/name/Aharonovweaknessmeasureme ntPhysRevA.41.11.pdf, and A. Parks, D. Cullin, and D. Stoudt, “Observation and Measurement of an Optical Aharonov-Albert-Vaidman effect”, Proc. R. Soc. Lond. A 454, 2997-3008 (1998), available at http://www.jstor.org/stable/53338 and at http://rspa.royalsocietypublishing.org/content/454/1979/2997.full.pdf.
Optical sensors using surface plasmon resonance (SPR) have been used for the direct detection of bio-molecules at surfaces since the mid-1980s. Such SPR sensors are generally comprised of three integrated portions: the optical detection component (ODC), the liquid management component (LMC), and the collection surface component (CSC). More specifically, typical SPR sensors are total internal reflection devices with a thin gold or silver film deposited upon the surface of a high dielectric medium. This represents the front interface, and that associated with the other side of the film is the rear interface.
When a beam of monochromatic transverse magnetic light is incident from the high dielectric medium upon the metallic film interface at an angle θ greater than or equal to the critical angle such that the light's magnetic field vector is parallel to the interface surface, an optically induced longitudinal oscillation of free electrons in the metal film resonantly transfers energy from the light to the surface plasmon wave propagating along the interface. This interaction is sensitive to changes in the reflective index of the medium at the rear interface (e.g., produced by bio-molecules introduced by the LMC that adhere to a metallic film which serves as the CSC) and yields a reduction in the intensity of the reflected light as a response to changes in the reflective index.
Consequently, the presence of bio-molecular species at the rear interface is heralded by changes in the light intensity reflected at an angle at or near θ. Such optical SPR sensors are generally referred to as attenuated total reflection (ATR) devices. The SPR phenomenon is described by B. Liedberg et al., “Surface Plasmon Resonance for Gas Detection and Biosensing”, Sensors and Actuators 4, 299-304 (1983).